There are several different levels of microcontrollers and microcontroller systems. Some are very small, chip-size devices to which you have to connect your own electronics. Others are larger, composed of several components and ports for input output, ready to plug right into other devices. Here is a short introduction.

Higher level microcontrollers will have a simple hardware interface to other devices (usually a plug or a couple of wires), and a simpler programming language, if at all. They will also usually be the most expensive of microcontrollers, because someone else has done the work for you. Lower level microcontrollers will require more work, both in terms of hardware connections (you will have to build your own circuits to interface them to other devices), and in terms of programming (you will need to use a lower level programming language like C or assembler). However, lower level processors are generally cheapest and most flexible in terms of what you can make them do. (via)

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